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Welding defects and discontinuities
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Discontinuities, including different types of cracks, can occur during welding of every type of steel. However, they can always be avoided. The Hardox® and Strenx® steel grades do not have any particular sensitivity to the discontinuities described in this context compared to other types of high strength steels.

Some types of discontinuities can be called defects. The meaning of these two terms differs to some extent.

  • A discontinuity is an interruption of the physical structure of the weldment
  • A defect is a discontinuity that causes the weldment to be unable to meet the specified requirements of the structure

Consequently, a defect needs to be removed and corrected in the structure. Other types of discontinuities can thereby be allowed in the same. In other words, a certain kind of discontinuity is a defect in certain structures and in others not.

Here are 11 typical discontinuous with a short texts about:

  • Possible causes
  • Suitable actions to avoid them
Expand all

Sagging or weld concavity

Cause

  • too high travel speed
  • number of beads too few
  • welding in downhill position

Remedial actions

  • reduce the travel speed
  • use sufficient number of beads
  • switch to Pa position (horizontal)

Porosity

Cause

  • Impurities in the joint (moisture, oil, corrosion, etc.)
  • Disturbing breeze
  • Too high gas flow
  • Too low gas flow
  • Shielding gas contaminated (equipment)
  • Injector effect
  • Surface coating (zinc, primer)

Remedial actions

  • Keep the joint free from any impurities
  • Control the equipment
  • Control the gas flow
  • Welding technique (torch angle)
  • Remove surface coating

Lack of penetration or root defect

Cause

  • Too small joint angle
  • Too small gap
  • Too large root face
  • Wrong welding technique
  • Too low heat input


Remedial actions

  • Increase the joint angle (45 – 60°)
  • Increase the gap    
  • Adapt the root face in relation to the heat input (1 – 2 mm)
  • Decrease the oscillation of the electrode
  • Increase the heat input

Excessive penetration

Cause

  • Too large gap
  • Too small root face
  • Too high heat input
  • Wrong welding technique


Remedial actions

  • Decrease the root gap
  • Increase the root face
  • Decrease the heat input
  • Increase the oscillation of the electrode

Undercut

Cause

  • Too high travel speed
  • Incorrect oscillation technique
  • Incorrect torch angle
  • Too high voltage
  • Too high heat input


Remedial actions

  • Decrease the travel speed
  • Use small stops at the end of oscillation
  • Neutral or a small forehand angle is beneficial
  • Decrease the voltage
  • Reduce the heat input

Hot crack or solidification crack

Cause

  • Weld bead too deep in relation to the width
  • High C, S, P, Nb pick-up
  • Too high travel speed
  • Large root gap


Remedial actions

  • Make sure that the width/depth-ratio of the weld exceeds about 1.0
  • The joint must be free from impurities
  • Reduce the welding speed
  • Reduce the root gap

Pipe

Cause

  • Wrong welding technique


Remedial actions

  • Use a proper welding technique. reverse and re-ignite to fill up the crater. larger beads/cross sections, might require a short cooling time (2 – 3 s) before the crater is filled.

Root concavity

Cause

  • Wrong welding technique in position welding
  • Too large root face


Remedial actions

  • Adjust torch angle and reduce the heat input
  • Use a root face of max 1.5 – 2 mm


Incompletely filled groove

Cause

  • Too high travel speed
  • Number of beads too few
  • Misplaced weld bead


Remedial actions

  • Reduce the travel speed
  • Use sufficient number of beads
  • Make sure that the weld bead covers the groove

Spatter

Cause

  • Too high voltage in comparison to the wire feed speed
  • Surface impurities
  • Magnetic arc blow
  • Coating (primer, zinc)


Remedial actions

  • Decrease the voltage level
  • Make sure that the surface is free from impurities
  • Weld towards the ground clamp
  • Grind away the surface coating

Lack of fusion

Cause

  • Travel speed too low (weld metal starts to flow in front of the arc)
  • Travel speed too high
  • Arc voltage too low
  • Too long “stick out” distance
  • Contact tip worn out
  • Insufficient inter-run cleaning
  • Welding in inclining position (downhill)


Remedial actions

  • Increase the travel speed
  • Decrease the travel speed
  • Increase the arc voltage
  • Decrease the stick out distance
  • Replace the contact tip
  • Remove the surface slag prior to next run
  • Adjust the travel speed in relation to the position